Cardiac pacemakers are known in the art to generate and apply pacing pulses to heart failure patients. Originally such cardiac pacemakers paced the heart at a fixed rate programmed in the cardiac pacemaker by the patient's physician.
However, the human body has an automatic regulatory mechanism that increases the cardiac output when the metabolic demand is increased, such as during increased patient activity and exercise. This increased cardiac output thereby enables sufficient transport of oxygen and removal of waste products in the patient body.
Rate-adaptive cardiac pacemakers have therefore been proposed to mimic this natural regulatory mechanism of the human body. The rate-adaptive cardiac pacemakers thereby increase the pacing rate at increased levels of metabolic activity. Various solutions have been presented in order to determine an appropriate rate increase in response to the increase in metabolic activity.
U.S. Pat. No. 4,436,092 discloses an exercise-responsive cardiac pacemaker which physiologically controls the pacing rate of a heart by sensing the venous blood temperature in the right ventricle of the heart. A temperature sensor produces an output signal which is sent to an algorithm which represents the mathematical function between venous blood temperature and the heart rate in a healthy heart.
US 2006/0265019 and US 2009/0287270 disclose rate-adaptive pacemakers that dynamically adjust their pacing rate based on a change in exertion level of the patient.
WO 97/18010 discloses a rate-adaptive pacemaker that sets a pacing rate based on the amplitude of the sensor signal from an activity sensor. The pacing rate is additionally modified based on the morphology of the sensor signal in terms of the quotient between the area of the sensor signal above a baseline and the area of the sensor signal below the baseline. This morphology-based correction of the pacing rate enable differentiation between activity levels when exercising on a leveled surface, up stairs or down stairs.
There is, though, still a need for a cardiac pacing that better mimics the natural regulatory mechanism in response to patient activity and exercise.